RFR: 8254167 G1: Record regions where evacuation failed to provide targeted iteration [v9]

[Albert Mingkun Yang]

On Tue, 7 Sep 2021 04:27:01 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> This is another try to optimize evcuation failure for regions.
>> I record evacuation failed regions, and iterate these regions directly rather than iterate the whole cset.
>> The implementation reuses and refactors some of the existing data in g1CollectedHeap (_regions_failed_evacuation, _num_regions_failed_evacuation), and records these regions in an array, and iterate this array later in post evacuation phase.
>> 
>> I have 2 implementations:
>> 
>> - 1) CHT (Initial version)
>> - 2) bitmap (latest version, reuse _regions_failed_evacuation in g1CollectedHeap)
>> 
>> This implementation does not consider work distribution as mentioned in JDK-8254167 yet. But seems it already get better&stable performance gain than origin. We could improve it further later if work distribution is necessary.
>> 
>> I will attach the perf data in JBS.
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix merging issues

src/hotspot/share/gc/g1/g1CollectedHeap.cpp line 2329:

> 2327: }
> 2328: 
> 2329: void G1CollectedHeap::par_iterate_regions_array_part_from(HeapRegionClosure* cl,

This method essentially apply a closure to all elements in `[offset, length)` of `regions`. I wonder if we can pass `&regions[offset]` and `length-offset` to this method. Then this method can work on the whole array, and figuring out the starting index for each worker becomes trivial, `worker_id * array_len / #workers`. It's not obvious to me why the calculation in this patch guarantees balanced start index.

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PR: https://git.openjdk.java.net/jdk/pull/5272